7.5.2 Basic Route Filtering

7.5.2 Basic Route Filtering

Filtering of routing information allows control of paths used by a
router to forward packets it receives. A router should be selective
in which sources of routing information it listens to and what routes
it believes. Therefore, a router MUST provide the ability to
specify:

On which logical interfaces routing information will be accepted
and which routes will be accepted from each logical interface.

Whether all routes or only a default route is advertised on a
logical interface.

Some routing protocols do not recognize logical interfaces as a
source of routing information. In such cases the router MUST provide
the ability to specify

from which other routers routing information will be accepted.

For example, assume a router connecting one or more leaf networks to
the main portion or backbone of a larger network. Since each of the
leaf networks has only one path in and out, the router can simply
send a default route to them. It advertises the leaf networks to the
main network.